Process for color reduction of dye wastewater

Abstract

A highly colored dye wastewater is treated by a sequence of steps to obtain a color reduction of 90 percent or more. The method requires acidifying the wastewater and adding a cationic flocculant. A reducing agent is then, optionally, added to further reduce the color value of the wastewater and produce an oxidation-reduction potential of at least -200 and, generally, about -400 to -800. The reducing agent is, preferably, either a hydrosulfite or both a bisulfite and an alkali metal borohydride.

I claim: 
     
       1. A process for reducing a color value of a wastewater containing a soluble organic dye, said process comprises: adjusting said wastewater to an acidic pH; and   admixing said wastewater with a sufficient quantity of a cationic flocculant from a quaternary ammonium condensation polymer to form a floc with said soluble organic dye,   admixing a reducing agent into said flocculated wastewater in a amount sufficient to attain an oxidation-reduction potential end point of at least -200, said admixing of said reducing agent being performed in one of two conditions, said two condition being as follows: a first condition wherein said reducing agent is a member selected from the group consisting of an alkali metal hydrosulfite, an alkaline earth hydrosulfite, and mixtures of these; and   a second condition wherein said reducing agent is a combination of:   a member selected from the group consisting of an alkali metal bisulfite, an alkaline earth bisulfite, and mixtures of these; and   an alkali metal borohydride, said alkali metal borohydride being a member selected from the group consisting of lithium borohydride, sodium borohydride, potassium borohydride, and mixtures of these; and     separating said flocculated soluble organic dye from said wastewater.   
     
     
       2. The process of claim 1, wherein said admixing of said reducing agent occurs before said admixing of said cationic flocculant. 
     
     
       3. The process of claim 1, wherein said admixing of said reducing agent occurs simultaneously with said admixing of said cationic flocculant. 
     
     
       4. The process of claim 1, wherein said admixing of said reducing agent occurs after said admixing of said cationic flocculant. 
     
     
       5. The process of claim 1, wherein said flocculant is a condensation product of epichlorohydrin, ethylenediamine, and dimethylamine. 
     
     
       6. The process of claim 1, wherein said adjusting of said pH of said wastewater provides a pH of about 5.0 to about 6.0. 
     
     
       7. The process of claim 1, wherein said flocculant is admixed in an amount to provide a concentration of about 50 to 3000 parts per million in said wastewater. 
     
     
       8. The process of claim 7, wherein said flocculant is admixed in an amount to provide a concentration of about 1000 to 2000 parts per million in said wastewater. 
     
     
       9. The process of claim 1, wherein said flocculant is a polydiallyldimethyl ammonium chloride. 
     
     
       10. The process of claim 1, wherein said alkali metal borohydride is added to said wastewater subsequent to admixing with said bisulfite. 
     
     
       11. The process of claim 1, wherein said reducing agent is sodium hydrosulfite. 
     
     
       12. The process of claim 1, wherein said reducing agent is a combination of sodium bisulfite and said alkali metal borohydride, said alkali metal borohydride is sodium borohydride. 
     
     
       13. The process of claim 1, wherein said flocculant and said reducing agent are added in sufficient amounts to reduce the color value of said wastewater at least 90 percent. 
     
     
       14. The process of claim 1, wherein said soluble organic dye is a member selected from the group consisting of azo dyes, acid dyes, indigo dyes, mordant dyes, reactive dyes, basic dyes, direct dyes, and combinations of these. 
     
     
       15. A process for reducing a color value of a wastewater containing a soluble organic dye, said process comprises: adjusting said wastewater to an acidic pH;   admixing said wastewater with a sufficient quantity of a cationic flocculant from a quanternary ammonium condensation polymer to form a floc with said soluble organic dye;   admixing said flocculated wastewater with at least one reducing agent in a sufficient amount to attain an oxidation-reduction potential end point of -400 to -800 said admixing of said reduction agent being performed in one of two conditions, said two conditions being as follows: a first condition wherein said reducing agent is a member selected from the group consisting of an alkali metal hydrosulfite, an alkaline earth hydrosulfite, and mixtures of these; and   a second condition wherein said reducing agent is a combination of:   a member selected from the group consisting of an alkali metal bisulfite, an alkaline earth bisulfite, and mixtures of these; and   an alkali metal borohydride, said alkali metal borohydride being a member selected from the group consisting of lithium borohydride, sodium borohydride, potassium borohydride, and mixtures of these; and     separating said flocculated soluble organic dye from said wastewater.   
     
     
       16. The process of claim 15, wherein said flocculant is a condensation product of epichlorohydrin, ethylenediamine, and dimethylamine. 
     
     
       17. The process of claim 15, wherein said adjusting of said pH of said wastewater provides a pH of about 2.0 to about pH 6.9. 
     
     
       18. The process of claim 17, wherein said adjusting of said pH of said wastewater provides a pH of about 5.0 to about pH 6.0. 
     
     
       19. The process of claim 15, wherein said flocculant is admixed in an amount to provide a concentration of about 50 to 3000 parts per million in said wastewater. 
     
     
       20. The process of claim 19, wherein said flocculant is admixed in an amount to provide a concentration of about 1000 to 2000 parts per million in said wastewater. 
     
     
       21. The process of claim 15, wherein said flocculant is a polydiallyldimethyl ammonium chloride. 
     
     
       22. The process of claim 15, wherein said alkali metal borohydride is added to said wastewater subsequent to said admixing with said bisulfite. 
     
     
       23. The process of claim 15, wherein said reducing agent is sodium hydrosulfite. 
     
     
       24. The process of claim 15, wherein said reducing agent is a combination of said sodium bisulfite and said alkali metal borohydride, said alkali metal borohydride is sodium borohydride. 
     
     
       25. The process of claim 15, wherein said flocculant and said reducing agent are added in sufficient amounts to reduce said color value of said wastewater at least 90 percent. 
     
     
       26. The process of claim 15 further comprising: filtering said wastewater subsequent to said admixing with said reducing agent.   
     
     
       27. A process for reducing a color value of a wastewater containing a soluble organic dye, said process comprises: adjusting said wastewater to a pH of about 2.0 to about 6.9;   admixing a sufficient quantity of a cationic flocculant from a quaternary ammonium condensation polymer to form a floc in said pH adjusted wastewater with said soluble organic dye;   admixing a reducing agent into said flocculated wastewater in an amount sufficient to attain an oxidation-reduction potential end of point of at least -200, said admixing of said reducing agent being performed in one of two conditions, said two conditions being as follows: a first condition wherein said reducing agent is a member selected from the group consisting of an alkali metal hydrosulfite, an alkaline earth hydrosulfite, and mixtures of these; and   a second condition wherein said reducing agent is a combination of:   a member selected from the group consisting of an alkali metal bisulfite , an alkaline earth bisulfite, and mixtures of these; and   an alkali metal borohydride, said alkali metal borohydride being a member selected from the group consisting of lithium borohydride, sodium borohydride, potassium borohydride, and mixtures of these; and     separating said flocculated soluble organic dye from said wastewater.   
     
     
       28. The process of claim 27, wherein said cationic flocculant is a condensation polymer of epichlorohydrin, dimethylamine, and ethylenediamine. 
     
     
       29. The process of claim 27, wherein said reducing agent is sodium hydrosulfite. 
     
     
       30. The process of claim 27, wherein said reducing agent is a combination of sodium bisulfite and said alkali metal borohydride, said alkali metal borohydride is sodium borohydride. 
     
     
       31. The process of claim 27, wherein said reducing agent is added in a sufficient amount to produce an oxidation-reduction potential of about -500 to -700. 
     
     
       32. The process of claim 27, wherein said reducing agent is added in an amount to provide a concentration of up to 5,500 parts per million in said wastewater. 
     
     
       33. The process of claim 27, wherein said flocculant is added in an amount to provide a concentration of about 50 to 2000 parts per million in said wastewater. 
     
     
       34. A process for reducing a color of a wastewater containing a soluble organic dye, said processing consisting essentially of: adjusting said wastewater to a pH of about 5.0 to 6.0;   admixing said acidified wastewater with a polymeric quaternary ammonium condensation polymer of epichlorohydrin, diethylamine, and ethylenediamine to form a floc with said soluble organic dye;   admixing said wastewater with at least one reducing agent to produce an oxidation-reduction potential of at least -200, said admixing of said reducing agent being performed in one of two conditions, said two conditions being as follows: a first condition wherein said reducing agent is a member selected from the group consisting of an alkali metal hydrosulfite, an alkaline earth hydrosulfite, and mixtures of these; and   a second condition wherein said reducing agent is a combination of:   a member selected from the group consisting of an alkali metal bisulfite, an alkaline earth bisulfite, and mixtures of these; and   an alkali metal borohydride, said alkali metal borohydride being a member selected from the group consisting of lithium borohydride, sodium borohydride, potassium borohydride, and mixtures of these; and     separating said flocculated soluble organic dye from said wastewater.   
     
     
       35. The process of claim 34, wherein the step of admixing said flocculant is in an amount to provide a concentration of about 50 to 3,000 parts per million in said wastewater. 
     
     
       36. The process of claim 35, wherein the step of admixing said flocculant is in the amount to provide a concentration of about 1000 to 2,000 parts per million in said wastewater. 
     
     
       37. The process of claim 34, wherein the step of admixing said reducing agent is in an amount to provide a concentration of up to 5,500 parts per million in said wastewater. 
     
     
       38. The process of claim 34, wherein said reducing agent is sodium hydrosulfite. 
     
     
       39. The process of claim 34, wherein said reducing agent is a combination of sodium bisulfite and a member selected from the group consisting of sodium borohydride, lithium borohydride, potassium borohydride, and mixtures of these. 
     
     
       40. The process of claim 39, wherein said reducing agent is added in a sufficient amount to provide said wastewater with an oxidation-reduction potential of -400 to -800.